ABSTRACT Colorectal cancer is the second leading cause of cancer deaths in the United States. At least 5% of colon cancer cases are linked to known high-penetrant genetic factors, while approximately 30% of cases are correlated with low penetrant genes and lifestyle factors that include a diet high in red meat consumption. Carcinogens found in charred red meat include heterocyclic aromatic amines (HAAs), which become potent DNA damaging agents after activation by cytochrome P450 enzymes and N-acetyl transferases (NATs). However, it is unknown which individuals are most susceptible to HAAs and epidemiological studies often lack significance due to small sampling sizes. The overall goal of this project is to determine which genetic risk factors for colon cancer increase the genotoxicity of HAAs. Because many DNA metabolism and housekeeping genes are conserved from yeast to man, high throughput analysis of Saccharomyces cerevisiae (budding yeast) genes that confer resistance to carcinogens has identified human genes that confer resistance to environmental carcinogens. We have previously screened ~5,000 yeast single-gene deletion diploid strains and identified HAA resistant genes, including DNA repair, cell cycle and mitochondrial genes. Human homologues of two of these genes, RAD18 and NTG1, are risk factors for colon cancer. In the first aim, we will determine whether DNA adducts are repaired less efficiently in DNA repair mutants and identify sites in CAN1 that are most susceptible to HAA-mutagenesis. In the second specific aim, we will determine HAA resistance pathways using quantitative genetic interaction mapping. Additional genes that confer resistance will also be identified by high-throughput sensitive assays to measure cell growth and by molecular bar codes using high throughput sequencing. In the third aim we will determine whether selective cytochrome P450 and NAT gene polymorphisms linked to cancer confer higher levels of HAA-mediated genotoxicity. The information resulting from this project will aid health care providers in identifying individuals most at risk for colon cancer due to dietary carcinogens.